A highly specific and sensitive monoclonal antibody-based ELISA for the detection of circulating antigen in bancroftian filariasis

A monoclonal antibody, Og4C3, directed against antigens of Onchocerca gibsoni (but not phosphorylcholine) has been used in a sandwich ELISA to detect a circulating antigen of Wuchereria bancrofti in human serum. The interfering effect of host antibody was reduced by first boiling one part of serum for 5 min in the presence of three parts of 0.1 M Na2EDTA, pH 4.0. A total of 119 sera from individuals and 8 pooled sera from clinical and/or parasitologically defined cases of filariasis, plus 8 individual and 1 pooled endemic control sera, all from the filariasis serum bank of the World Health Organisation, as well as 20 non-endemic control sera, were screened with the assay. Circulating antigen was detected in serum from people infected with W. bancrofti but not Brugia malayi, B. timori, O. volvulus or Loa loa, and not in endemic or non-endemic controls. Of the 68 sera from W. bancrofti-infected subjects, 55/55 parasitologically confirmed and 12/13 clinically confirmed but amicrofilaraemic cases reacted in the assay. A weak but significant correlation (r2 = 0.4016) was found between numbers of microfilariae in blood and detectable levels of circulating antigen from patients with bancroftian filariasis.